Among American Indians/Alaska Natives (AI/AN), Oklahoma had the 5th highest age-adjusted incidence rate of any cancer in the US (584.3 per 100,000 in Oklahoma v. 304.8 per 100,000 in the US) from 1999-2012 and AI/ANs in the US rank poorly in cancer survival. In addition, Oklahoma ranks poorly in many health-related factors compared to other states in the US, including overall health, cancer mortality, lack of health insurance, obesity, physical inactivity, and smoking, among others, which may be related to cancer incidence and survival. In 1997, the Cherokee Nation established the first and only tribally-operated population-based Surveillance Epidemiology and End Results (SEER) cancer registry in the country, including cancer cases residing in the 14-county Cherokee Nation Tribal Jurisdictional Service Area (CNTJSA) in Northeastern Oklahoma. Many AI/ANs who reside in the CNTJSA receive treatment for their cancer at facilities outside of the Cherokee Nation health system. Thus, the CNCR needs to be linked with clinical treatment and outcomes data from health facilities both inside and outside of Cherokee Nation health system to obtain extensive follow- up and information on behavioral and other risk factors. The proposed Cherokee Nation Health Analytics Core (CNHAC) aims to build capacity by addressing the following specific aims: 1) Establish infrastructure at Cherokee Nation and the University of Oklahoma Health Sciences Center College of Public Health to develop the CNHAC through conversion of physical space, hiring data coordinators, providing computing resources, and development of a data access working group; 2) Develop policies and protocols for accessing and linking electronic health data from various health facilities including CNCR, Cherokee Nation EMR, OCCR, and MyHealth; 3) Link CNCR records with Cherokee Nation EMR and external health data from MyHealth to be used in future research studies; 4) Use the following research question focused on breast cancer to test the policies and protocols developed for secondary use of clinical data for research and to evaluate the validity and completeness of the data linkage: What factors influence adherence to standard of care for breast cancer treatment for women in Cherokee Nation?.